In an AHG test, control cells show three out of eight tubes negative after adding check cells. What is the likely error?

In an AHG test, control cells show three out of eight tubes negative after adding check cells. What is the likely error?

• A. Insufficient saline from automated cell washer
• B. Serum was omitted from the reaction
• C. Insufficient incubation period
• D. AOTA

Answer: (A)

In AHG testing, control cells (check cells) are used to verify that the antihuman globulin reagent is functioning properly. After adding the check cells, you expect to see agglutination in all reaction tubes if the test is being performed correctly. When only some of the control tubes become negative, it signals a technical issue during the test setup rather than a true antibody problem. Insufficient saline from the automated cell washer is a classic culprit. If the wash is not thorough enough, residual wash solution, cell debris, or unremoved serum components can interfere with the proper contact and cross-linking required for agglutination by AHG. This can yield a mixed pattern where a portion of the tubes fail to show the expected agglutination with the check cells, even though the AHG reagent is active. Therefore, inadequate saline wash disrupts the delicate balance needed for consistent AHG reactivity across all controls. If serum were omitted, you’d expect failing results across the board rather than a subset, and insufficient incubation typically weakens reactions uniformly rather than producing selective negatives. All of the above is not indicated by the observed pattern, so the most plausible explanation is the insufficient saline wash.

In AHG testing, control cells (check cells) are used to verify that the antihuman globulin reagent is functioning properly. After adding the check cells, you expect to see agglutination in all reaction tubes if the test is being performed correctly. When only some of the control tubes become negative, it signals a technical issue during the test setup rather than a true antibody problem.

Insufficient saline from the automated cell washer is a classic culprit. If the wash is not thorough enough, residual wash solution, cell debris, or unremoved serum components can interfere with the proper contact and cross-linking required for agglutination by AHG. This can yield a mixed pattern where a portion of the tubes fail to show the expected agglutination with the check cells, even though the AHG reagent is active. Therefore, inadequate saline wash disrupts the delicate balance needed for consistent AHG reactivity across all controls.

If serum were omitted, you’d expect failing results across the board rather than a subset, and insufficient incubation typically weakens reactions uniformly rather than producing selective negatives. All of the above is not indicated by the observed pattern, so the most plausible explanation is the insufficient saline wash.